The present invention relates generally to a hermetic scroll-type compressor and, more particularly, to such a compressor having intermeshing fixed and orbiting scroll members, wherein it is necessary to provide an axial force on the orbiting scroll member to bias it toward the fixed scroll member for proper sealing therebetween.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed pockets. When one of the scroll members is orbited relative to the other, the pockets travel between a radially outer suction port and a radially inner discharge port to convey and compress the refrigerant fluid.
It is generally believed that the scroll-type compressor could potentially offer quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design problems persist that have prevented the scroll compressor from achieving wide market acceptance and commercial success. For instance, during compressor operation, the pressure of compressed refrigerant at the interface between the scroll members tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the opposite scroll member. Such leakage causes reduced compressor operating efficiency and, in extreme, cases, can result in an inability of the compressor to operate.
Attempts in prior art scroll-type compressors to resist the separating force applied to the scroll members during operation of the compressor, in order to prevent the aforementioned leakage, have not proven to be entirely satisfactory. One approach is to axially preload the scroll members toward each other with a force sufficient to resist the dynamic separating force. However, this approach results in high initial frictional forces between the scroll members and/or bearings when the compressor is at rest, thereby causing difficulty during compressor startup. Another prior art approach involves assuring close manufacturing tolerances for component parts and having the separating force borne by a thrust bearing. This approach not only requires an expensive thrust bearing, but also involves high manufacturing costs in maintaining close machining tolerances.
Another prior art scroll-type compressor design, disclosed in many prior art patents, involves the provision of an intermediate pressure chamber behind the orbiting scroll member, whereby the intermediate pressure creates an upward force to oppose the separating force. Such a design recognizes the fact that suction pressure behind the orbiting scroll member is insufficient to oppose the separating force, while discharge pressure behind the orbiting scroll member results in too great an upward force causing rapid wear of the scroll wraps and faces. However, establishing an intermediate pressure between suction pressure and discharge pressure requires that an intentional leak be introduced between an intermediate pressure pocket and a discharge pressure region. Such a leak results in less efficient operating conditions for the compressor.
Several other prior art scroll compressor designs, directed to controlling the upward force on the orbiting scroll member to oppose the separating force, have utilized a combination of gaseous refrigerant at suction pressure and gaseous refrigerant at discharge pressure for exposure to respective areas on the backside of the orbiting scroll member. In such compressor designs, various seal means have been utilized to separate the respective gas pressure regions. A primary disadvantage of this type of design is the difficulty encountered in sealing between gas regions at different pressures. Consequently, prior art compressors of this general design require elaborate sealing means and closer manufacturing tolerances, thereby increasing the cost of the compressor.
The present invention is directed to overcoming the aforementioned problems associated with scroll-type compressors, wherein it is desired to provide an axial force on the orbiting scroll member to facilitate sealing and prevent leakage between the interfitting scroll members.